Idle speed control valve control system

ABSTRACT

An outboard motor comprises an engine mounted within an engine compartment. The engine comprises an induction system having an induction passage extending between an air intake box to a combustion chamber. A throttle valve is positioned along the passage. A bypass passage communicates with the passage at a location between the throttle valve and the combustion chamber. An adjustable valve controls flow through the bypass passage. The adjustable valve is opened as the throttle valve is opened or as the engine speed is increased. The adjustable valve is closed when the throttle valve is rapidly closed or when the engine speed is rapidly decreased.

PRIORITY INFORMATION

This application is based on and claims priority to Japanese Patent Application No. 11-293055, filed Oct. 14, 1999, the entire contents of which is hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to idle speed controls for internal combustion engines used in marine applications. More specifically, the present invention relates to such systems in which throttle bypass levels are adjusted based on throttle valve positioning or engine speed.

2. Related Art

Outboard motors are powered by engines contained within an engine compartment of the outboard motor. The outboard motors are conventionally attached to watercraft to power the watercraft in a forward or reverse direction. As is known, the engine of the outboard motor is subject to increased loading when compared to that of an automobile, for instance. This increased loading generally results from the nature of the outboard motor and the environment of use of the outboard motor.

The engines that power the outboard motors may contain an intake system featuring a bypass passage. The bypass passage typically is linked to the intake system upstream and downstream of a throttle control valve. As is known, the throttle control valve controls the amount of air flowing through the induction system into the engine for combustion. When the throttle control valve is closed, the air flow rate is minimized and when the throttle control valve is opened, the flow rate through the induction system can be somewhat controlled. The use of a bypass passage allows air to bypass the throttle control valve for supply to the engine even when the throttle control valve is closed. In some instances, an ISC, or idle speed control valve, is positioned along the bypass passage. The ISC valve can be used to fine tune the idling engine speed when the throttle control valve is in a closed position.

Conventional ISC valves are designed to open when the throttle valve suddenly closes following a period of high speed operation. It is thought that by opening the ISC valves when the throttle valve closes, misfiring and stalling can be obviated or greatly reduced. Generally speaking, the ISC valves are closed when the throttle valve is opened and when the engine speed is low. The ISC valves are opened when the throttle valve is closed and when the engine speed is high. In some applications, the ISC valves can be suddenly opened during high speed operation of the engine and then gradually closed after the engine speed decreases below a preset level.

The positioning of the idle speed control valve often is controlled by inexpensive step motors. The inexpensive step motors typically have a slow response characteristic. In other words, the command to move is followed by a slight delay before the movement occurs. In addition, these motors cause the valves to move relatively slowly and incrementally.

With reference now to FIG. 6, a conventional ISC valve control strategy implemented in such a system is illustrated in broken lines. As illustrated in this arrangement, the ISC valve traditionally remains closed while the throttle valve is opening. The ISC valve remains in the closed position until the throttle angle is rapidly decreased (i.e., the throttle valve closes under the biasing force of a spring, such as when the opening provided by an operator controlled actuator is removed). Once the throttle angle is rapidly decreased, the ISC valve slowly opens under the control of the stepper motor. Because of the slow opening rate of the idle speed control valve, the air flow through the induction system does not properly match the desired change of the engine speed resulting from the rapid change in throttle position. Accordingly, the engine can stall or misfire due to an inadequate supply of intake air. One way of correcting this is to provide an idle speed control valve in which the ISC valve opens more rapidly for each input signal to the stepper motor. A drawback from this approach is that a large ISC valve is required and the larger ISC valves increase cost and weight.

Accordingly, an arrangement is desired in which the idle speed control valve is positioned to provide an adequate air supply upon rapid closure of an associated throttle valve.

SUMMARY OF THE INVENTION

Accordingly, an idle speed control system is desired in which an idle speed control valve is opened as a throttle valve is opened and in which the idle speed control valve is closed when the throttle valve is rapidly closed.

One aspect of the present invention involves a small watercraft comprising an engine disposed within an engine compartment. The engine comprises a cylinder body. At least one cylinder bore is formed in the cylinder body. A piston is mounted for reciprocation within the cylinder bore. A cylinder head is disposed over a first end of the cylinder bore. A crankcase member is disposed over a second end of the cylinder bore. An output shaft is disposed at least partially within a crankcase chamber at least partially defined by the crankcase member. The output shaft powers an output device and a speed sensor is adapted to sense an output speed of the engine. A combustion chamber is defined at least partially within the cylinder bore between the cylinder head and the piston. An intake conduit communicates with the combustion chamber. A throttle valve is disposed within the intake conduit. A throttle valve sensor is capable of sensing a position of the throttle valve. A bypass passage communicates with the intake conduit at a location between the throttle valve and the combustion chamber. An idle speed control valve is disposed along the bypass passage. A controller electrically communicates with the idle speed control valve, the speed sensor and the throttle valve sensor. The controller is adapted to open the idle speed control valve as a function of at least one of a first input signal from the speed sensor indicative of an increase in engine speed and a second input signal from the throttle valve sensor indicative of an the throttle valve is opened.

Another aspect of the present invention involves a method of controlling movement of an idle speed control valve. The method comprises detecting a throttle angle, sensing an engine speed, determining a desired idle speed control valve positioning based upon the sensed engine speed, detecting an idle speed control valve positioning, moving the idle speed control valve if the desired idle speed control valve positioning differs from the detected idle speed control valve positioning.

A further aspect of the present invention involves a method of controlling an idle speed control valve in an engine for a watercraft. The method comprises sensing a throttle angle, determining a desired idle speed control valve positioning based upon the sensed throttle angle, detecting an idle speed control valve positioning, moving the idle speed control valve if the desired idle speed control valve positioning differs from the detected idle speed control valve positioning.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present invention will now be described with reference to the drawings of several preferred embodiments, which embodiments are intended to illustrate and not to limit the invention, and in which figures:

FIG. 1 is a schematic illustration of an engine and a portion of a watercraft shown in phantom having a control system arranged and configured in accordance with certain features, aspects and advantages of the present invention;

FIG. 2 is a schematic illustration of an induction system featuring a bypass passage;

FIG. 3 is a schematic illustration of a section of an idle speed control valve arranged and configured in accordance with certain features, aspects and advantages of the present invention;

FIG. 4 is a graphical depiction of valve position over time illustrating movement of the valve using a stepper motor;

FIG. 5 is a graphical depiction of an idle speed control valve opening position relative to a throttle angle illustrating a controlled opening of the idle speed control valve in response to an opening of the throttle valve;

FIG. 6 is a graphical depiction of an idle speed control valve control arrangement having certain features, aspects and advantages in accordance with the present invention; and

FIG. 7 is a flow diagram of a control routine having certain features, aspects and advantages in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference now to FIG. 1, a portion of an outboard motor 20 attached to a watercraft 22 is illustrated. In addition, in FIG. 1, a portion of an engine 24 is shown in schematic cross-section. Furthermore, a portion of a fuel supply system 26, portions of the outboard motor 20, the engine 24 and the fuel system 26 are interconnected by an ECU or other suitable controller 28. While the present invention will be described in the context of an outboard motor that is attached to a watercraft, it should be apparent to those of ordinary skill in the art that the present invention can be used in other environments. For instance, the present invention may find utility in personal watercraft, small water vehicles, jet boats and the like. In particular, due to the unique operating characteristics of water vehicles, the present invention is particularly designed for use in such applications.

With continued reference to FIG. 1, the outboard motor 20 is attached to a transom 30 of the watercraft 22. In the illustrated arrangement, the outboard motor 20 is attached to the transom 30 with a mounting bracket 32. Any suitable mounting bracket 32 can be used to attach the outboard motor 20 to the watercraft 22. The mounting bracket 32 preferably allows the outboard motor 20 to be tilted and trimmed about a generally horizontal axis and preferably allows the outboard motor 20 to be steered about a generally vertical axis. Such arrangements are well known to those of ordinary skill in the art.

In the illustrated arrangement, an outboard motor position sensor 34 is connected to the outboard motor 20 and to the ECU 28 to provide a signal to the ECU 28 which is indicative of a relative positioning of the outboard motor 20 and the watercraft 22. In the illustrated arrangement, the position sensor 34 is hardwired to the ECU 28. It is anticipated that any number of quick disconnect electrical couplings can be provided between the sensor 34 and the ECU 28. In addition, it is anticipated that the connection between the sensor 34 and the controller 28 can have any suitable configuration. For instance, but without limitation, the two components can be connected by a physical wire, by infrared signals, by radio waves or in any other suitable manner. Of course, other sensors will be described below and such interconnections can be used with any of the sensors and the ECU 28. Moreover, the ECU 28 preferably is designed to control various valves, injectors and ignition systems using a variety of control signals. The control signals can be sent between the ECU 28 and the receptor component in any of these manners as well.

The outboard motor 20 in the illustrated outboard motor 20 generally comprises a lower unit 36 and a driveshaft housing 38. While not shown, a powerhead can be positioned above, and can be supported by, the driveshaft housing 38. The powerhead generally comprises a protective cowling which encases the engine 24 and provides a protective environment in which the engine can operate.

The engine 24 preferably is of the four-cycle, multi-cylinder type. In some arrangements, the engine 24 can comprise six cylinders arranged in two banks in a V-6 configuration. In other arrangements, such as that illustrated schematically in FIG. 2, the engine 24 comprises four cylinder bore arranged inline in a single bank. It should be noted that the present invention may find that some utility with engines having other operating principles. For instance, some of the features of the present invention may find applicability to two-stroke and rotary-type engines.

With continued reference to FIG. 1, the illustrated engine preferably comprises a cylinder block 40 in which one or more of the cylinder bores 42 are defined. It is anticipated that the cylinder block 40 can be replaced by individual cylinder bodies that define the cylinder bores 42. In addition, the cylinder bores 42 may receive a sleeve or other suitable treatment to reduce friction between the cylinder block 40 and a piston 44, which is arranged for reciprocation within the cylinder bore 42.

The piston 44 is mounted for reciprocation within the cylinder bore 42. The piston 44 is connected by a connecting rod 46 to a throw 48 of a crankshaft 50. As the piston 44 is driven up and down within the cylinder bore 42, a crankshaft 50 is driven for rotation about a rotational axis. A suitable speed sensor 52 preferably is provided to sense the engine speed, as indicated by the rotational speed of the crankshaft 50. In the illustrated arrangement, a pulsar coil 54 is connected to the crankshaft 50 and the speed sensor 52 operates to detect the rotational speed of the pulsar coil. The signals generated by the speed sensor 52 are then transmitted to the ECU 28 for use in manners which will be described.

A cylinder head assembly 56 preferably is positioned atop of the cylinder block 40. The cylinder head 56, in combination with the piston 44 and the cylinder bore 42, defines a combustion chamber 58. It should be noted that the cylinder block 40 in the illustrated arrangement contains a sensor 60 which outputs a signal indicative of a temperature of coolant flowing through a cooling jacket associated with the cylinder block 40. Of course, the sensor 60 can be positioned in other positions such that it outputs a signal indicative of an operating temperature of the engine 24 to the ECU 28.

An intake passage 62 is defined through a portion of the cylinder head 24. In some arrangements, more than one intake passage 62 may be defined through the cylinder head 24 into the combustion chamber 58. An intake control valve 64 can be designed to control the flow of intake air through the passage 62 into the combustion chamber 58. Movement of the intake valve 64 is controlled, in the illustrated arrangement, with a cam shaft 66. Such arrangements are well known to those of ordinary skill in the art.

With reference now to FIG. 2, air is inducted into the induction system through an air intake box 70. The air drawn into the air intake box 70 is passed to the combustion chamber 58 via a set of intake pipes 72. The intake pipes 72 extend between the air box 70 and the associated intake passages 62 for each individual combustion chamber 58. Flow through the intake pipes 72 is controlled with a throttle valve 74. In the illustrated arrangement, a number of throttle valves 74 are positioned on a single rod 76 and are controlled with a single actuator 78. The actuator 78 controls the movement of the valves 74 about a rotational axis in response to changes in operator demand. The operator can change the positioning of the throttle valves 74 by operating an accelerator pedal or an accelerator lever in any manner well known to those of ordinary skill in the art. Of course, the throttle valves can be separately controlled or a single throttle valve can control the flow through the entire induction system.

In the illustrated arrangement, a bypass passage 80 is provided between or the intake box 70 and the individual runners 72 extending to the cylinder head 56. The bypass passage 80 is designed to communicate with each of the illustrated intake runners 72. The bypass passage 80 opens into the individual runners 72 downstream of the throttle control valve 74 such that when the throttle control valves 74 are closed, air may be supplied to the intake runners 72 through the bypass passage 80 under the control of an idle speed control valve 82. In some arrangements, multiple valves 82 can be provided to correspond with the multiple runners 72. The idle speed control valve 82 can be opened and closed to vary the level of flow through the associated bypass passage 80.

The idle speed control valve 82 can be moved using an actuator 84 associated with the valve 82, which will be described in more detail below. In the illustrated arrangement, the actuator 84 comprises a stepper motor. In some configurations, however, the actuator 84 may comprise a solenoid or other suitable actuator mechanism. In the illustrated arrangement, the actuator 84 is connected to the ECU 28 to receive signals from the ECU 28 that are generated in accordance with certain features, aspects and advantages of the present invention.

Air inducted through the induction system is mixed with fuel provided through the fuel supply system 26. In the illustrated arrangement, the fuel supply system 26 draws fuel from a fuel tank 88 that is positioned within the watercraft 22 in the illustrated arrangement. The fuel is drawn from the fuel tank 88 through a supply line 90 with a first low pressure fuel pump 92. In some arrangements, the low pressure fuel pump 92 may be driven by pressure variations within the crankcase. The fuel is drawn by the fuel pump 92 and supplied to a fuel filter 94 in manners well known to those of ordinary skill in the art. In addition, fuel from the fuel filter 94 is drawn by a second low pressure pump 96 for deposit into a vapor separator 98. The vapor separator 98 preferably includes a float 100 that operates to control the level of fuel within the vapor separator 98 at any given moment.

A fuel pump 102 is provided within the vapor separator 98 to provide fuel from the vapor separator 98 to the engine for combustion. In the illustrated arrangement, a pressure regulating fuel return 104 is provided. The pressure regulating fuel return 104 returns fuel when the pressure within a fuel supply line 106 exceeds a preset level.

The fuel through the fuel supply line 106 is supplied under high pressure to a fuel injector 108. The fuel injector 108 in the illustrated arrangement is designed for indirect injection. That is, the fuel injector 108 injects fuel into the induction system at a location outside of the combustion chamber 58. In some arrangements, however, the fuel injector 108 may be disposed for injection directly into the combustion chamber 58.

Fuel may be bypassed from the fuel injector 108 through a return line 110. The return line 110 maintains a flow of fuel between the vapor separator 98 and the fuel injector 108. The flow of fuel decreases the influence of combustion heat generated within the combustion chamber 58 upon the fuel and reduces vaporization of fuel. In addition, by returning the fuel to the vapor separator 98, the pressure of the fuel supplied to the fuel injector 108 can be controlled. Of course, the fuel injector 108 can be controlled using the ECU 28 in a manner known to those of ordinary skill in the art. This is represented by the control signal illustrated in FIG. 1.

The air fuel mixture drawn into the combustion chamber 58 can be ignited with any suitable ignition component 112. In the illustrated arrangement, a sparkplug 112 is disposed with an electrode positioned within the combustion chamber 58. The sparkplug 112 can be fired in accordance with any suitable ignition strategy and in the illustrated arrangement, is controlled through the ECU 28.

Following combustion, the exhaust gases can be removed from the combustion chamber 58 through an exhaust passage 114 that extends from the cylinder head 56. The exhaust passage 114 includes at least one exhaust port that is disposed in the cylinder head 56 adjacent to the combustion chamber 58.

An exhaust control valve 116 controls the opening and closing of the exhaust port to allow exhaust gases to flow from the combustion chamber 58. The exhaust control valve 116 is opened and closed with an exhaust cam shaft 118 or in any other suitable manner. The exhaust gases then can be transferred from the exhaust passage 114 to the atmosphere or body of water in which the watercraft is operating in any suitable manner. For instance, in some arrangements, the exhaust gases may be routed through the driveshaft housing 38 into the lower unit 36 and out through a through-the-hub discharge.

Rotational power from the crankshaft 50 preferably is provided to a driveshaft 120. The driveshaft 120 is used to power an output device such as a propeller 122. In the illustrated arrangement, a forward-neutral-reverse bevel gear transmission 124 is interposed between the driveshaft 120 and a propeller shaft 126. The propeller shaft 126 is splined or otherwise suitably connected to the propeller 122. Movement of the propeller 122 also can be controlled by the transmission 124 in any other suitable manner.

In the illustrated arrangement, a shift rod 128 is provided to shift the transmission 124 between forward, neutral and reverse. A position sensor 130 is provided that emits a signal to the ECU 28. The signal indicates a relative position of the transmission 124. For instance, the signal may indicate that the transmission is in a forward position, a reverse position or a neutral position. In some configurations, the signal may indicate that the transmission is either engaged or disengaged. In other words, the signal may indicate that the transmission is in a forward or reverse state or, alternatively, that the transmission is disengaged and in a neutral state.

Several other components also can be driven by the driveshaft 120. In the illustrated arrangement, a lubricant pump 132 is provided. The lubricant pump 132 draws lubricant from a lubricant reservoir 134. The lubricant from the reservoir 134 is provided to the engine 24 for lubrication through a supply line 136. Preferably, a variety of sensors are provided in a lubrication system to indicate an operational state of the lubrication system. For instance, in the illustrated arrangement, a pressure sensor 138 as well as a temperature sensor 140 are provided. These sensors 138, 140 provide signals to the ECU 28.

In addition, the driveshaft 120 powers a water pump 142. The water pump 142 draws cooling water from within the body of water in which the watercraft is operating and provides it to the engine and various other components. In the illustrated arrangement, the coolant provided by the cooling pump 142 can be provided to a variety of cooling jackets. In this manner, the coolant can cool the engine as well as various operating components related to the engine and the watercraft and can be returned to the body of water in which the watercraft is operating. Of course, in some arrangements, a reservoir containing coolant can be provided from which the coolant is drawn and returned.

The illustrated arrangement also features a number of other sensors that communicate with the ECU 28. For instance, a throttle valve position sensor 144 is provided that emits a signal indicative of the positioning of the throttle valves 74. The signal may indicate the percentage opening of the throttle valves. For instance, a throttle valve that is 0% open is closed. While a throttle valve that is 80% open is substantially wide open. The illustrated ECU 28 also communicates with an induction pressure sensor 146. The induction pressure sensor 146 can be arranged to detect the pressure within an induction system associated with the engine 24. In some arrangements, a sensor 146 may be provided to a single runner 72 or may be provided to each runner 72 individually. Moreover, the ECU 28 receives a signal from an atmospheric pressure sensor 148. The atmospheric pressure sensor 148 communicates with the ECU 28 and provides a signal indicative of the pressure in the environment in which the watercraft is operating. An oxygen detection sensor 150 may be provided in the exhaust system to indicate an operational status of the engine 24. The oxygen detection sensor can be used to detect how complete combustion is within the combustion chamber 58 in any manner known to those of ordinary skill in the art.

With reference now to FIG. 3, an exemplary idle speed control valve 82 is illustrated therein. In the illustrated arrangement, the actuator 84 comprises a rotor 152 and a stator 154. Preferably, the rotor and the stator are components of a stepper motor. While the present invention will be described as using a stepper motor as the actuator, solenoids and other suitable actuators also can be used.

The rotor 152 preferably comprises a threaded inner surface 156 that mates with a threaded outer surface 158 that is connected to the valve 82. In addition, a biasing member 160, or spring in the illustrated arrangement, biases against a portion of the valve 82. As the rotatable member or rotor 152 rotates relative to the stator 154, the idle speed control valve 82 is extended into and retracted out of the passage defined by the bypass passage 80. In other words, a first direction of rotation of the rotor 152 relative to the stator 154 drives the valve 82 downward while a second direction of rotation drives the valve upward, as illustrated in FIG. 8. Of course, upward and downward are relative to the figure and should not limit the present invention. The biasing member 160, which in the present arrangement happens to be a spring but need not be, urges the valve in a downward orientation to reduce the likelihood that the valve 82 is stuck in a retracted position.

With reference now to FIG. 4, a typical movement of the idle speed control valve under the influence of the actuator 84 is graphically illustrated therein. In this arrangement, the valve is moved from a closed position to an open position over time. As illustrated, a number of steps are required to move the valve between the two positions. The steps are separated by time and the movements occur quite rapidly in each step. The result is a very controlled movement of the valve between a closed and an open position and vice versa. The downside to the controlled movement, however, is that the movement tends to be relatively slow.

With reference now to FIG. 5, a graphical illustration of the idle speed control valve opening percentage relative to the throttle angle is presented. As illustrated in this exemplary embodiment, the idle speed control valve preferably is controllably opened as a throttle angle is opened. In other words, while the throttle angle is slowly opened from a closed position to a wide open position, the ISC valve is similarly opening with the largest amount of opening occurring during about the first 10° of throttle movement. Advantageously, this allows the idle speed control valve to open during just a slight advancement of the throttle angle. As can be seen from the graphical depiction of FIG. 5, the ISC valve continues to open at a slightly less rapid rate between about 10° and about 50° of throttle angle. In this configuration, the ISC valve maintains a steady opening rate while the throttle angle is opened from about 10° to about 50°. After about 50° of throttle angle, however, the opening of the ISC valve greatly decreases in the illustrated arrangement. The opening of the ISC valve advantageously is controlled based upon the positioning of the throttle valve.

With reference now to FIG. 6, a graphical depiction of a control arrangement having certain features, aspects and advantages of the present invention is illustrated therein. In this arrangement, the ISC valve is being opened while the throttle angle is increasing. In other words, while the throttle valve is being opened, the ISC valve also is being opened. As indicated in FIG. 5, the ISC valve opens more quickly or more rapidly during the first portions of throttle valve movement. For instance, the ISC valve and the throttle valve are opened over time. At a particular moment in time, T1 in the illustrated arrangement, the throttle valve is rapidly closed. By rapidly closed, it is intended to mean that the biasing force holding open the throttle valve is removed or that the throttle valve is returned to a closed position under the control of a return spring rather than being slowly released under operator control. This is meant to differentiate between a controlled throttle angle decrease, such as when the operator slowly decreases the throttle angle, and a rapid throttle angle decrease, wherein the operator simply releases the actuator member controlling the throttle valve.

In the illustrated arrangement, when the throttle valve angle rapidly decreases, the ISC valve is slowly closed under the control of the actuator 84. This arrangement, therefore, differs from previous arrangements in that the valve is closed when the throttle valve is rapidly closed instead of being opened when the throttle valve is rapidly closed.

With reference now to FIG. 7, a control routine that is capable of implementing a control strategy that achieves control similar to that described graphically in FIG. 6 is illustrated therein. With reference now to FIG. 7, the routine begins by detecting a throttle angle (see S-1). After the throttle angle has been detected, a target value of the ISC valve opening is determined (see S-2). This determination is based upon the throttle angle which has been detected in S1 in the illustrated arrangement. In particular, the target value of the ISC valve opening can be chosen based upon a preprogrammed control map in which the ISC valve opening is related to the throttle angle.

After determining the target value of the ISC valve opening, the target value is compared with the currently sensed value of the ISC valve opening position (see S-3). If the target value and the current value are the same, then the routine begins again by detecting the throttle angle. However, if the target value is different from the current value, the ISC valve is moved (see S-5) and the routine begins again by detecting the throttle angle. Of course, the movement can open or close the ISC valve depending upon the controlled movement of the throttle valve. For instance, if the throttle valve is controllably opened, then the ISC valve is opened a corresponding amount and if the throttle valve is controllably closed, then the ISC valve is closed a corresponding amount. The illustrated arrangement, therefore, provides a control strategy whereby the throughput of air can be adequately maintained when the throttle valve is rapidly closed. In addition, the ISC valve can be used to provide a metered amount of air in some applications such that the amount of air being provided at substantially all times includes at least a portion of bypass air.

While the above-described arrangement controls ISC valve position based upon throttle position, the ISC valve position also can be controlled based on engine speed or other proxies for engine speed. For instance, a flow rate of air through the induction system can be sensed and the ISC valve position can be varied based upon the sensed flow rate. More preferably, the speed sensor output is used and the controller manipulates the ISC valve based upon the sensed engine speed. Of course, regardless of the variable that the valve position is a function of, the valve position preferably is adjusted during an opening period based upon that variable. More preferably, the valve is closed at a controlled rate when the throttle valve is suddenly closed. Sudden closure of the throttle valve can be sensed through the throttle valve sensor or through large changes in variables such as air flow, for instance.

Although the present invention has been described in terms of certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired and certain steps of the control routine can be combined, subdivided or interlaced with other operations. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow. 

What is claimed is:
 1. A small watercraft comprising an engine disposed within an engine compartment, the engine comprising a cylinder body, at least one cylinder bore being formed in said cylinder body, a piston being mounted for reciprocation within said cylinder bore; a cylinder head being disposed over a first end of said cylinder bore, a crankcase member being disposed over a second end of said cylinder bore, an output shaft being disposed at least partially within a crankcase chamber at least partially defined by said crankcase member, said output shaft powering an output device, a speed sensor being adapted to sense an output speed of said engine, a combustion chamber being defined at least partially within said cylinder bore between said cylinder head and said piston, an intake conduit communicating with said combustion chamber, a throttle valve being disposed within said intake conduit, a throttle valve sensor being capable of sensing more than two positions of said throttle valve, a bypass passage communicating with said intake conduit at a location between said throttle valve and said combustion chamber, an idle speed control valve being disposed along said bypass passage, a controller electrically communicating with said idle speed control valve, said speed sensor and said throttle valve sensor, said controller being adapted to open said idle speed control valve as a function of at least one of a first input signal from said speed sensor indicative of an increase in engine speed and a second input signal from said throttle valve sensor indicative of said throttle valve being opened.
 2. The small watercraft of claim 1 further comprising a stepper motor drivingly connected to said idle speed control valve, wherein said controller electrically communicates with said idle speed control valve through said stepper motor.
 3. The small watercraft of claim 1, wherein the engine further comprises at least a second cylinder bore and a second combustion chamber, a second intake conduit communicating with said second combustion chamber and a second throttle valve disposed along said second intake conduit, said bypass passage communicating said second intake conduit at a location between said second throttle valve and said second combustion chamber, said bypass passage comprising a first branch that communicates with said intake conduit, a second branch that communicates with said second intake conduit and a main body that communicates with said first branch and said second branch, said idle speed control valve being positioned along said main body.
 4. The small watercraft of claim 1, wherein said engine forms a portion of an outboard motor.
 5. The small watercraft of claim 1 further comprising a hull and said engine compartment being positioned outside of said hull.
 6. The small watercraft of claim 5, wherein said hull comprises a transom and said engine compartment is defined by a cowling of an outboard motor that is connected to said transom.
 7. A method of controlling movement of an idle speed control valve, the method comprising detecting a throttle angle, sensing an engine speed, determining a desired idle speed control valve positioning based upon said sensed engine speed, detecting an idle speed control valve positioning, moving said idle speed control valve if said desired idle speed control valve positioning differs from said detected idle speed control valve positioning, wherein movement of said idle speed control valve is a function of engine speed if said engine speed is increasing.
 8. The method of claim 7, wherein said function of engine speed comprises at least two different rates.
 9. The method of claim 8, wherein said function of engine speed comprises three different rates.
 10. The method of claim 1 further comprising detecting if said throttle angle is rapidly decreased and closing said idle speed control valve if said throttle angle is rapidly decreasing.
 11. The method of claim 10, wherein said idle speed control valve is closed at a single rate.
 12. A method of controlling movement of an idle speed control valve, the method comprising detecting a throttle angle, sensing an engine speed, determining a desired idle speed control valve positioning based upon said sensed engine speed, detecting an idle speed control valve positioning, moving said idle speed control valve if said desired idle speed control valve positioning differs from said detected idle speed control valve positioning, wherein a proxy is used to determine engine speed.
 13. The method of claim 12, wherein said proxy is said detected throttle angle.
 14. A method of controlling an idle speed control valve in an engine for a watercraft, the method comprising sensing a throttle angle of a throttle valve, determining a desired idle speed control valve positioning based upon said sensed throttle angle when said throttle valve is open, detecting an idle speed control valve positioning, moving said idle speed control valve if said desired idle speed control valve positioning differs from said detected idle speed control valve positioning.
 15. The method of claim 14, wherein movement of said idle speed control valve is a function of throttle angle if said sensed throttle angle is increasing.
 16. The method of claim 15, wherein said function of throttle angle comprises at least two different rates.
 17. The method of claim 16, wherein said function of throttle angle comprises three different rates.
 18. The method of claim 14 further comprising detecting if said throttle angle is rapidly decreased and closing said idle speed control valve if said throttle angle is rapidly decreasing.
 19. The method of claim 18, wherein said idle speed control valve is closed at a single rate. 